For example, as a storage case used for packaging or storing an electronic device, there is known a paper carton made by folding and assembling a cardboard paper sheet. For example, Patent Literature 1 discloses a packing box including a main case having a bottom-plate, both side-plates at long sides, and both side-walls at short sides, and a top-plate connected openably and closably with at an upper end of the side-plate at one short side.